In recent years, the ink jet recording has increasingly been used in facsimiles, word processors, terminal printers, etc., since it causes no noise, needs no procedures for development and fixation, enables high-speed recording, and easily makes multi-color recording. Among others, the development is now being forwarded to color printers based upon the ink jet recording method for the purpose of making color hard copies from color displays.
The ink jet color printers have heretofore been used in a color graphics field wherein seven colors (yellow, magenta, cyan, red, green, blue, black) are used. In recent years, however, the development is now being forwarded to high-resolution color printers which give full-color copies of high quality comparable to that achieved by gravure printing or silver salt photography, the so-called pictorial color copies.
Ink jet recording is fundamentally advantageous in being capable of using plain paper, the so-called PPC (Plain Paper Copies). However, any satisfactory results are not yet obtained, if ordinary plain papers are used as the sheets for ink jet recording especially for multi-color recording.
The sheets for ink jet color recording are required to possess the basic properties that:
1. Ink dots are of a round shape, are not faded in color, and make a sharp contrast to their circumferences, thus leading to high resolution; PA0 2. Ink dots are high in both color density and color saturation; PA0 3. They absorb rapidly ink in a large amount, dry rapidly, and show good multi-color recording properties, by which, when ink dots are superposed upon each other, the outermost ink is prevented from flowing out; and PA0 4. They show a dimensional stability with no fear of suffering curling, waving or deforming which may be caused by recording. PA0 Chemical Substance V: Acrylic cation resin having a quaternary ammonium base PA0 Chemical Substance VI: Acrylic anion resin having an acrylate group PA0 Chemical Substance VII: Carboxybetaine type acrylic ampholytic resin PA0 (A) Preparation of the Ultraviolet or Radiation Curing Type Resin PA0 (B) Preparation of the Ultraviolet or Radiation Curing Type Antistatic Agents
In particular, a major technical problem to be solved by those skilled in the art is to simultaneously achieve the opposite properties, one being ink absorptivity dominating the speed of ink drying and the other being dot spreading accompanied with low resolution. Generally, as the ink absorptivity of a recording sheet increases, the ink dot spreading increases so that the shape of ink dots is distorted, resulting in lowering of resolution. In addition, an ink tendency to penetrate deeply into the paper layer leads to lowering of color density and color saturation.
More particularly, when used the multi-color ink jet printer, the recording sheet used is required to possess high ink absorptivity, since the ink droplets of various colors are deposited onto the same or neighboring portions thereof within a very short time. Otherwise an unabsorbed amount of ink will flow, so that the resulting printed image will not only be unclear but will also be stained.
Fundamentally, normal paper such as fine paper may be used as the ink jet recording sheet. In this case, however, one skilled in the art should really regulate or select various paper properties such as the degree of sizing, air permeability, density, smoothness, and dimentional stability such as elongation in water, etc. depending upon the recording systems involved, the conditions applied or the ink used. On the other hand, it is substantially unfeasible to make color recording of high picture quality, now demanded, only through optimizing the above-mentioned properties of the normal paper. For that reason, an examination has been made of ink jet recording sheets having on their surface a coated layer wherein an optimized combination of pigments and binders is applied in order to meet the aforesaid fundamental requirements. However, there is not yet found any ink jet recording sheet for high picture quality, which is satisfactory in terms of recording performances as well as water resistance, weather resistance, dimensional stability and like other factors.
Recently, it is also demanded to use as the backing sheets not only papers but also impregnated paper sheets, plastic films, synthetic paper sheets, and metal sheets, which are water-resistant. Referring concretely to, for instance, increasing demand for color displays to be used with the computers for personal use, it is desired to develop transparent films, which make ink jet color recording possible, in order to use color hard copies with OHP (Overhead Projectors). However, any plastic films such as transparent polyester films used as the OHP films cannot be applied for that purpose, since, unlike paper, they are hydrophobic and, hence, are of no ink absorptivity at all. This also holds for other substrates such as impregnated papers, metalized papers, synthetic papers, metal sheets or the like.
As discussed above, some technical limits are placed on the development of ink jet recording sheets based on such new substrate materials, when it is attempted on the basis of the structural concept of the conventional ordinary of coated papers.